Like everyone else, endurance athletes worry about their weight. And, like everyone else, endurance athletes diet periodically. We know that a pound contains about 3,500 calories, so if we eat 1,000 calories less each day, more than two pounds will magically disappear each week. And, since we are generally impatient, we push the daily caloric deficit to help us get to our goal weight faster. For athletes, however, the consequences of reducing caloric intake by 750-1,000 calories per day can be significant.

An often-ignored observation was made almost 30 years ago by researchers at Rockefeller University. They looked at the effect of calorie deficit on weight loss. As might be expected, the highest caloric deficit produced the greatest weight loss. What wasn't expected, however, was where the weight loss was coming from.

Everyone who goes on a diet is expecting to lose body fat. The researchers found that people who practiced moderate caloric restriction tended to lose the weight as fat. Ninety-one percent of the loss was fat and 9% was lean body mass, or muscle. When the subjects engaged in a diet involving severe calorie restriction, fat represented 48% of the loss and muscle represented 42%. Expressed another way, the greater the daily calorie restriction, the greater the loss of muscle mass.

This research also explains why the longer one is on a severe calorie restriction diet, the harder it is to keep losing weight. As the body loses more muscle mass there is a dramatic effect on overall energy metabolism, since a resting muscle cell burns almost eight times more energy per day than a fat cell. As you lose muscle mass, you have to eat even less to keep the weight loss going.

The final consequence of a crash diet begins the moment you stop the diet. Your body, having just gone through a period of food deprivation, goes into a hyper-storage mode when you resume normal eating. As we all know, hyper-storage is simply a nutritionist's way of saying fat accumulation. In anticipation that there might be another food deprivation cycle in the future, your body stores a higher percentage of food calories as fat.

Ironically, moderate to severe calorie restriction, which results in counter-adaptations by your body, is unnecessary. In fact, a recent study shows that a group who had a 200-calorie-a-day deficit had the same weight loss at six months as a group who had a 750-calorie-a-day deficit. More importantly, diets that have small daily caloric deficits (200-300 calories) don't activate the countermeasure that ultimately will make you less fit.

FREE RADICALS AND MUSCLE FATIGUE

You probably know that the muscles produce lots of free radicals during exercise. You may also know that free radicals produced during and after exercise damage muscle cells and contribute to post-exercise soreness. What you might not know is that free radicals also contribute to muscle fatigue during exercise. That’s right: free radicals can make you bonk. How they do it is not fully understood yet, but recent science makes it clear they do.

Free radicals are not all bad, though. The same compounds that make you bonk during exercise also stimulate physiological adaptations to exercise that make you fitter. Because of this, you don’t necessarily want to load up on a bunch of antioxidant supplements to squash the production of free radicals in your workouts. In other words, you don’t want to overdo your consumption of supplemental antioxidants to the point where they become a crutch that prevents your muscles from fully responding to your training.

Until we know more, your best bet is to focus on maintaining a healthy diet that helps strengthen your body’s own natural antioxidant defenses. For example, glutamine is a natural amino acid that increases the concentration of glutathione, the body’s “master antioxidant”, in muscle cells. Good sources of glutamine include meats, fish, eggs, dairy products, beans, beets, spinach and some recovery products.

SHOULD YOU EAT LIKE A CAVEMAN?

One of the latest trends in endurance sports nutrition is the Paleo Diet. It was developed by Loren Cordain, Ph.D., whose book, The Paleo Diet, was published in 2002. It became popular with endurance athletes after a sequel, The Paleo Diet for Athletes, was published three years later.

So what is the Paleo Diet? The authors believe that we humans are healthiest and function best when we eat exclusively those foods that our ancient ancestors ate during the Paleolithic Age, which covers the entire span of our evolution from roughly 2.5 million years ago to about 12,000 years ago. The rationale behind this way of eating is that our species evolved in adaptation to the foods we ate. Thus, our genes are specifically designed to use these nutrition sources. Any food types that entered our diet after the main work of our evolution was done—including grains and dairy products, which the Paleo Diet forbids—cannot be used as efficiently and effectively by our bodies.

There is plenty of anecdotal evidence in support of the Paleo Diet. Athletes who switch to it report fat loss and increased energy levels. However, there is no scientific evidence that the Paleo Diet is healthier or better for endurance performance than less restrictive healthy diets, such as vegetarian, Mediterranean, and DASH. Remember, the best diet is not just wholesome but also sustainable.